4(1)On the making, by the authority levying the rates, of their first such demand, and on the making by them of any subsequent such demand, the amount of the rates for any rental period shall if necessary be recalculated on the basis that the rates for the relevant rating period will be such as appears from the information given in the demand and any previous demands.E+W
(2)Any such recalculation shall not affect the ascertainment of the rates for any rental period beginning more than 6 weeks before the date of the service of the demand giving rise to the recalculation.